All references, including any patents or patent applications, cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art, in Australia or in any other country.
One of the most important economic groups of yeasts are of the genus Saccharomyces, strains of which are employed in the brewing, baking, winemaking, distilling and various other yeast-dependent industries. Species of Saccharomyces are as defined phylogenetically by Kurtzman (2003) FEMS Yeast Research 3:417-432, and include S. cerevisiae, S. paradoxus, S. mikatae, S. cariocanus, S. kudriavzevii, S. pastorianus and S. bayanus. Saccharomyces spp. are some of the most effective microorganisms for converting sugars such as glucose, fructose, sucrose and maltose to biomass, and for fermenting these sugars to ethanol. As a consequence, Saccharomyces spp., and in particular Saccharomyces cerevisiae, is one of the most widely used microorganisms in industrial processes. For example, in the beer brewing, distilling and wine industries, Saccharomyces are used to ferment sugars such as glucose, fructose, sucrose and/or maltose into ethanol. In the fuel ethanol industry, Saccharomyces cerevisiae strains are chosen for their ability to rapidly convert high concentrations of sugars such as glucose, fructose, sucrose and maltose into high amounts of ethanol. In the baking industry, Saccharomyces cerevisiae strains are used primarily for their ability to produce carbon dioxide from sugars such as glucose, fructose, sucrose, and/or maltose in order to leaven bread. Other applications of Saccharomyces cerevisiae include production of yeast extracts and other flavour and aroma products, sources of enzymes such as invertase, production of various biochemicals, intermediates, proteins, amino acids, ribonucleic acid and nucleotides co-factors and vitamins.
Millions of tonnes of yeast are grown each year in industrial processes. Therefore, the ability of Saccharomyces to grow on abundant and renewable carbon sources is important in terms of economic production of yeast biomass for industrial purposes and for economic production of byproducts from yeast metabolism. In particular the ability of Saccharomyces to grow on waste byproducts of other industrial processes is of environmental and economic value. Thus, for example, baker's yeast biomass is often produced by growing yeast on molasses which is a waste product of the sugar production process, or on glucose- and maltose-rich syrups derived from starch hydrolysis industry.